The present invention relates to apparatus and methods which provide data by which personnel can monitor the operation of a fluid flow system.
Leakage of fluid from a fluid flow system for toxic, corrosive, or flammable chemicals poses a potential safety hazard for employees of an industrial plant and inhabitants of the surrounding community. Leakage from a fluid flow system, such as a pipeline for transportation of crude oil from offshore to onshore stations, poses a risk of damage to the environment. Leakage during transportation of fuel in a pipeline results in diminution of the available supply of fuel and adds to the energy crisis. In the interests of safety, ecology, and energy conservation, operation of fluid flow systems must be monitored so that prompt corrective action can be taken in the event of loss due to leakage.
Unnecessary refining loss is a major concern of industry. Production control personnel must know the refining loss in order to adjust operation of the refining process to improve efficiency and to reduce refining loss to an optimum figure. In the interest of efficiency, refining processes must be monitored so that prompt corrective action can be taken to minimize loss due to refining.
Moreover, if loss due to leakage or refining is minimized, waste of significant dollar amounts of material is avoided.
In all fluid flow systems operation can be monitored by comparing the amount of fluid that is input to the fluid flow system with the amount of fluid that is output from the fluid flow system. If more fluid flows in than out, the occurrence of a loss is indicated. If more fluid flows out than in, the occurrence of a gain is indicated. Actually, "gain" is negative loss and is hereinafter included within the meaning of the term "loss" unless it is expressly stated otherwise.
For many years leakage detection systems employed instantaneous flow measurements at spaced stations along a pipeline and determined the difference between these instantaneous measurements to obtain an indication of loss between any two locations monitored. By instantaneous measurement is meant a measurement of a characteristic of the fluid flow system, such as fluid flow, at a particular moment in time. Such leakage detection systems assumed a hydraulic stability that cannot and does not occur in practice. Consequently, sudden disturbances in the operation of the fluid flow system resulted in erroneous loss indications.
In an attempt to improve upon such leakage detection systems, the monitoring system of Fowler et al, U.S. Pat. No. 3,505,513, totals the fluid that flows through remote stations at various locations along a pipeline over an interval of time. Upon interrogation from a master station at the end of the time interval each remote station transmits its total to the master station. The master station calculates the difference between totals at successive stations. The calculation is compared to a preset limit to obtain an indication of loss due to leakage.
The system of Fowler et al indicates a short-term loss for the pipeline since the calculation is based on totals for an interval of operation rather than instantaneous measurements. Fowler et al recognizes the fact that noise or sudden disturbances, such as sharp pressure or temperature changes, which occur during an interval of operation, can cause a spurious loss indication, especially where the monitoring system is set to detect a small leak. Fowler et al proposes that a counter be employed so that the monitoring system responds only to a predetermined number of consecutive short-term loss calculations.
Erroneous loss indications can, however, result unless the minimum number of consecutive short-term loss calculations cannot occur during a period of time less than the stabilization time for the pipeline. If the stabilization time is taken into account, however, a large amount of fluid can be lost before personnel take corrective action since no alarm due to an actual change in the operation of the pipeline results for a predetermined number of consecutive intervals of operation of the pipeline.
The monitoring system of Sullivan, U.S. Pat. No. 3,909,596, employs stations at various locations in a refinery which generate counts which are temperature compensated and which may be moisture compensated based on laboratory analysis. After one of the stations reaches a predetermined count, it enables a difference counter. The difference counter counts simultaneously with the second station until the second station reaches the predetermined number of counts. The difference count is displayed as an indication of loss due to refining.
The monitoring system of Sullivan indicates a short-term loss for a refining process, analogous to the short-term loss for a pipeline by Fowler et al, since each difference count relates to an interval of operation. Sullivan recognizes the fact that noise or sudden disturbances, such as sharp pressure changes, may cause a spurious loss indication. Sullivan proposes that the counters at the stations count predetermined ones of the signals generated by the stations to increase the period of time which is required to arrive at the difference count beyond the stabilization time of the refining process.
Since sudden disturbances during an interval of operation influence the loss for only that interval of operation, however, the indication of loss for the interval of operation can appear unreasonably high. Although the fluid flow system might actually have stabilized, personnel may react unnecessarily to the high loss indication to adjust operation of the refining process since in the event operation has not stabilized hesitation would result in waste of material.
It is an object of the present invention to provide apparatus and methods which generate a series of short-term losses in which each element of the series is determined on the basis of data for more than a single interval of operation, thereby eliminating spurious indications of loss due to sudden disturbances in the operation of the fluid flow system.
It is an associated object of the present invention to smooth sudden disturbances in the operation of the fluid flow system over a selectively variable number of short-term loss indications in the series.
It is also an associated object of the present invention to provide apparatus and methods to average changes in the operation of the fluid flow system over a selectively variable number of intermittent loss indications in the series for the purpose of displaying trends in the operation of the fluid flow system.
It is another object of the present invention to provide apparatus and methods which, in addition to generating a series of short-term losses, indicate an accurate overall loss for a period of operation of the fluid flow system.
It is an additional object of the present invention to provide apparatus and methods to correct fluid flow meter measurements to a standard temperature, moisture content, and flow meter calibration to assure the reliability of both the short-term and overall loss indications.